It is useful to know certain characteristics of a borehole for drilling operations. In order to gather information about the borehole, drillers often use a wireline or logging while drilling (LWD) tool that can retrieve data and produce logs or even images representing the characteristics of the formations penetrated by the borehole. An example of one such tool is a sonic logging tool, which operates by generating sonic pulses and measuring the time it takes for such pulses to propagate along the borehole. With such measurements, drillers are able to measure a variety of geological characteristics including formation density and porosity.
One of the properties that drillers may find important is sonic measure of formation brittleness. Moderately brittle formations may be expected to be easily fractured and hence more permeable to fluid flows. Ideally, the driller would like to position the borehole in a region where such permeability provides access to a reservoir of hydrocarbons. Highly brittle formations, on the other hand, may be expected to be unstable and prone to borehole cave-ins and collapse, a situation which could cause economic and environmental losses and even necessitate abandonment of the well. There do not appear to be any logging systems and methods available for providing drillers with suitable azimuthal formation brittleness measurements during the drilling process.